US20070018117A1 - Imaging mode for linear accelerators - Google Patents

Abstract

Some embodiments include reception of a first instruction to enter an imaging mode, and, in response to the first instruction, automatic performance of at least one of: reduction of a focal spot size of a radiation beam, movement of a flattening filter out of a path of the radiation beam, replacement of a first target for photon emission with a second target for photon emission, or movement of a scatter-reducing filter into the path of the radiation beam. Embodiments may further include reception of a second instruction to enter a first radiation treatment mode, and, in response to the second instruction, automatic performance at least one of: increase of a focal spot size of the radiation beam, movement of the flattening filter into the path of the radiation beam, replacement of the second target with the first target, or movement of the scatter-reducing filter out of the path of the radiation beam.

Description

BACKGROUND
• 1. Field
• The embodiments described herein relate generally to linear accelerators. More particularly, the described embodiments relate to linear accelerators providing multiple operating modes.
• 2. Description
• A linear accelerator produces electrons or photons having particular energies. In one common application, a linear accelerator produces a radiation beam used for medical radiation treatment. The beam may be directed toward a target area of a patient in order to destroy cells within the target area by causing ionizations within the cells or other radiation-induced cell damage.
• Radiation treatment plans are designed to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. However, designers of a treatment plan assume that relevant portions of a patient will be in a particular position relative to a linear accelerator during delivery of the treatment radiation. If the relevant portions are not positioned exactly as required by the treatment plan, the goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved. More specifically, errors in positioning the patient can cause the delivery of low radiation doses to tumors and high radiation doses to sensitive healthy tissue. The potential for misdelivery increases with increased positioning errors.
• Conventional imaging systems may be used to determine a patient position prior to treatment according to a particular radiation treatment plan. For example, a radiation beam is emitted by a linear accelerator, passes through a volume of the patient and is received by an imaging system. The imaging system generates a two-dimensional portal image of the patient volume, which can be used to determine whether the patient is in a position dictated by the particular treatment plan.
• The foregoing imaging systems may be both ineffective and inefficient. For example, the radiation beam generated by a linear accelerator for imaging may deliver a dose rate that is significantly less than a dose rate used for radiation treatment, but other characteristics of the beam may be unsuitable for imaging. Moreover, no efficient systems exist for changing these characteristics such that the resulting beam is suitable for imaging.
SUMMARY
• In order to address the foregoing, some embodiments provide a system, method, apparatus, and means to receive a first instruction to enter an imaging mode, and, in response to the first instruction, automatically perform at least one of: reducing a focal spot size of a radiation beam, moving a flattening filter out of a path of the radiation beam, replacing a first target for photon emission with a second target for photon emission, or moving a scatter-reducing filter into the path of the radiation beam. Embodiments may further include reception of a second instruction to enter a first radiation treatment mode, and, in response to the second instruction, automatic performance at least one of: increase of a focal spot size of the radiation beam, movement of the flattening filter into the path of the radiation beam, replacement of the second target with the first target, or movement of the scatter-reducing filter out of the path of the radiation beam.
• According to some aspects, the second instruction comprises an instruction to enter a photon radiation treatment mode, a third instruction is received to enter an electron radiation treatment mode, and, in response to the third instruction, the first target or the second target is automatically moved out of the path of the radiation beam so that neither the first target or the second target is in the path of the radiation beam.
• Some embodiments include an input device to receive a first instruction to enter an imaging mode, and a second instruction to enter a first radiation treatment mode, and an accelerator waveguide to emit a radiation beam. Also included in these embodiments is at least one of a first device to reduce a focal spot size of a radiation beam in response to the first instruction, and to increase a focal spot size of the radiation beam in response to the second instruction, a second device to move a flattening filter out of a path of the radiation beam in response to the first instruction, and to move the flattening filter into the path of the radiation beam in response to the second instruction, a third device to replace a first target for photon emission with a second target for photon emission in response to the first instruction, and to replace the second target with the first target in response to the second instruction, or a fourth device to move a scatter-reducing filter into the path of the radiation beam in response to the first instruction, and to move the scatter-reducing filter out of the path of the radiation beam in response to the second instruction.
• The appended claims are not limited to the disclosed embodiments, however, as those in the art can readily adapt the descriptions herein to create other embodiments and applications.
BRIEF DESCRIPTION OF THE DRAWINGS
• Embodiments will become readily apparent from consideration of the following specification as illustrated in the accompanying drawings, in which like reference numerals designate like parts, and wherein:
• FIG. 1 is a perspective view of a linear accelerator system according to some embodiments;
• FIG. 2 is a block diagram of a linear accelerator system according to some embodiments;
• FIG. 3 is a flow diagram of process steps pursuant to some embodiments;
• FIG. 4 is an outward view of an interface to receive instructions according to some embodiments;
• FIG. 5 is an outward view of an interface to receive instructions according to some embodiments;
• FIG. 6 is a block diagram of a linear accelerator system according to some embodiments;
• FIG. 7 is a block diagram of a linear accelerator system according to some embodiments;
• FIG. 8 is block diagram of a linear accelerator system according to some embodiments; and
• FIG. 9 is an outward view of an interface to receive instructions according to some embodiments.
DETAILED DESCRIPTION
• The following description is provided to enable a person in the art to make and use some embodiments and sets forth the best mode contemplated by the inventors for carrying out some embodiments. Various modifications, however, will remain readily apparent to those in the art.
• FIG. 1 is a perspective view ofsystem1 according to some embodiments. Shown arelinear accelerator10,operator console20,beam object30,imaging device40 and table50.System1 may be used to generate radiation for imaging and/or for medical radiation treatment. In this regard,beam object30 comprises a patient positioned to receive treatment radiation according to a radiation treatment plan.System1 may be employed in other applications according to some embodiments.
• In one example according to some embodiments, a first instruction to enter an imaging mode is received, and, in response to the first instruction, at least one of the following is automatically performed: reducing a focal spot size of a radiation beam, moving a flattening filter out of a path of the radiation beam, replacing a first target for photon emission with a second target for photon emission, or moving a scatter-reducing filter into the path of the radiation beam. Embodiments may further include reception of a second instruction to enter a first radiation treatment mode, and, in response to the second instruction, automatic performance at least one of: increase of a focal spot size of the radiation beam, movement of the flattening filter into the path of the radiation beam, replacement of the second target with the first target, or movement of the scatter-reducing filter out of the path of the radiation beam.
• Linear accelerator10 may deliver a radiation beam fromtreatment head101 toward a volume ofobject30 that is located at an isocenter ofaccelerator10. According to some embodiments, the radiation beam may comprise photon or electron radiation having various energies. Various implementations oftreatment head101 according to some embodiments are described below.
• Imaging device40 may comprise any system to acquire an image based on received photon radiation (i.e., X-rays) and/or electron radiation.Imaging device40 acquires images that are used before, during and after radiation treatment. For example,imaging device40 may be used to acquire images for diagnosis, verification and recordation of a patient position, and verification and recordation of an internal patient portal to which treatment radiation is delivered. As described above, the effectiveness of radiation treatment often depends on the quality of the acquired images.
• In some embodiments,imaging device40 is a flat-panel imaging device using a scintillator layer and solid-state amorphous silicon photodiodes deployed in a two-dimensional array. The RID1640, offered by Perkin-Elmer®, Inc. of Fremont, Calif., is one suitable device. In other embodiments,imaging device40 converts X-rays to electrical charge without requiring a scintillator layer. In such imaging devices, X-rays are absorbed directly by an array of amorphous selenium photoconductors. The photoconductors convert the X-rays directly to stored electrical charge that comprises an acquired image of a radiation field.Imaging device40 may also comprise a CCD or tube-based camera. Such an imaging device may include a light-proof housing within which are disposed a scintillator, a mirror, and a camera.
• Imaging device40 may be attached to gantry102 in any manner, including via extendible andretractable housing401. Gantry102 is rotatable around an axis before, during and after emission of the radiation beam. Rotation ofgantry102 may causetreatment head101 andimaging device40 to rotate around the isocenter such that the isocenter remains located betweentreatment head101 andimaging device40 during the rotation.
• Table50 supports object30 during radiation therapy. Table50 is adjustable to ensure, along with rotation ofgantry102, that a volume of interest is positioned betweentreatment head101 andimaging device40. Table50 may also be used to support devices used for acquisition of correction images, other calibration tasks and/or beam verification.
• Operator console20 includesinput device201 for receiving instructions from an operator andoutput device202, which may be a monitor for presenting operational parameters oflinear accelerator10 and/or interfaces for receiving instructions. Such instructions may include an instruction to enter an imaging mode and an instruction to enter a treatment mode.Output device202 may also present images acquired byimaging device40 to verify patient positioning prior to radiation treatment.Input device201 andoutput device204 are coupled toprocessor203 andstorage204.
• Processor203 executes program code according to some embodiments. The program code may be executable to controlsystem1 to operate as described herein. The program code may be stored instorage204, which may comprise one or more storage media of identical or different types, including but not limited to a fixed disk, a floppy disk, a CD-ROM, a DVD-ROM, a Zip™ disk, a magnetic tape, and a signal.Storage204 may, for example, store a software application to provide radiation treatment, radiation treatment plans, portal images, and other data used to perform radiation treatment. The other data may include sets of hard-coded parameters for various elements ofsystem1, or “soft pots”, that are associated with various functions ofsystem1. For example, one set of soft pots may be associated with an imaging mode, another set of soft pots may be associated with an X-ray treatment mode, and while another set of soft pots may be associated with an electron treatment mode.
• Operator console20 may be located apart fromlinear accelerator10, such as in a different room, in order to protect its operator from radiation. For example,accelerator10 may be located in a heavily shielded room, such as a concrete vault, which shields the operator from radiation generated byaccelerator10.
• Each of the devices shown inFIG. 1 may include less or more elements than those shown. In addition, embodiments are not limited to the devices shown inFIG. 1.
• FIG. 2 is a block diagram ofsystem1 showing internal elements oflinear accelerator10,operator console20, andimaging device40 according to some embodiments. Embodiments may differ from that shown inFIG. 2 and/or from that shown inFIG. 1.
• Linear accelerator10 ofFIG. 2 includeselectron source103 for injecting electrons intoaccelerator waveguide104.Source103 may comprise an electron gun including a heater, a cathode (thermionic or other type), a control grid (or diode gun), a focus electrode, an anode, and other elements. An injector current sourced byparticle source103 may be controlled by injector pulses received frominjector105.Injector105 may, in turn, receive trigger signals fromtrigger control106 and control the amplitude of the injector pulses by a control grid bias voltage applied tosource103.
• Accelerator waveguide104 includes cavities that are designed and fabricated so that electric currents flowing on their surfaces generate electric fields that are suitable to accelerate the electrons. The oscillation of these electric fields within each cavity is delayed with respect to an upstream cavity so that an electron is further accelerated as it arrives at each cavity.
• The oscillating electric fields within the cavities ofaccelerator waveguide104 are produced in part by an oscillating electromagnetic wave received byaccelerator waveguide104 fromRF power source107.Trigger control106 may controlRF power source107 to generate an electromagnetic wave having a selected power and/or pulse rate.RF power source107 may comprise any suitable currently- or hereafter-known pulsed power source. In some embodiments,RF power source107 comprises a magnetron.RF power source107 comprises a klystron and an RF driver in some embodiments.
• Accelerator waveguide104 mayoutput beam108 to bendingenvelope109.Beam108 includes a stream of electron bunches having various energies and bendingenvelope109 may comprise an evacuated magnet to bendbeam108 approximately two hundred seventy degrees.Bending envelope109 may also focusbeam108 and select one or more energies for output.
• Bending envelope109 may select an energy by establishing a magnetic field that will allow only electrons of a selected energy (or of a range of energies surrounding the selected energy) to turn two hundred seventy degrees and exit throughwindow110. Other bending angles and/or systems to select energies may be used.
• Window110 may comprise two metal foils with water flowing therebetween for cooling.Beam108 enterstreatment head101 after passing throughwindow110.Treatment head101 may comprise any number and arrangement of elements according to some embodiments.
• Treatment head101 ofFIG. 2 includes control unit111 which may receive control signals fromoperator console20. Control unit111 is coupled tobeam focuser112,target housing113 including hi-Z target114 and low-Z target115, flatteningfilter116, andother elements117. The depiction oftreatment head101 inFIG. 2 is not intended to indicate relative sizes or spatial relationships of the elements located therein, although some embodiments may be thus reflected.
• The couplings between control unit111 and each ofelements112 through117 may comprise mechanical and/or electrical couplings. One or more elements may reside between control unit111 and an element to which it is shown coupled inFIG. 2. In some embodiments, control unit111 comprises one or more separate elements, each of which is coupled to one or more ofelements112 through117. One or more ofelements112 through117 may be controlled directly byoperator console20 and/or by another device according to some embodiments.
• The elements oftreatment head101 may be configured based on an operating mode ofsystem1. For example, the elements may be configured in a first arrangement if an instruction is received to enter a treatment mode, and the elements may be configured in a second arrangement if an instruction is received to enter an imaging mode.FIG. 2 illustrates an arrangement used in a treatment mode according to some embodiments.
• Beam focuser112 may comprise any suitable system to receivebeam108 and to change a focal spot size thereof. The focal spot size may refer to the profile of the beam at a location where photon emission occurs within one oftargets113 and114. Generally, a smaller focal spot may be suitable for imaging while a larger focal spot may be suitable for delivering treatment.
• In some embodiments,beam focuser112 comprises deflector plates disposed adjacent to a path ofbeam108. Control unit111 may energize the deflector plates during emission ofbeam108 in order to create a desired focal spot size.Beam focuser112 may be used to increase the focal spot size for treatment in a case that the focal spot size would be unsuitably small in the absence ofbeam focuser112. Alternatively,beam focuser112 may be used to reduce the focal spot size for imaging in a case that the focal spot size would be unsuitably large in the absence ofbeam focuser112. Treatment head111 may include mechanical elements to movebeam focuser112 out of the path ofbeam108 if a selected operating mode does not require beam focusing.
• Target housing113 includes hi-Z (i.e., high atomic weight)target114, which may comprise Gold, Tungsten, or another suitable material. Upon receivingelectron beam108, such a target may generate photons having an energy spectrum suitable for radiation treatment. Low-Z (i.e., low atomic weight)target115 may comprise Carbon, Aluminum, or another suitable material. Such a target may generate photons having an energy spectrum suitable for imaging in response to receipt ofelectron beam108. The terms hi-Z and low-Z as used herein are not intended to indicate particular atomic weights, but only a relationship of the atomic weight oftarget114 to the atomic weight oftarget115.
• Target housing113 may comprise any suitable system to selectively placetarget114 ortarget115 in the path ofbeam108. Such placement may be controlled by control unit111.Target114 is shown placed in the path becausesystem1 is in an X-ray treatment mode according to some embodiments.
• Flatteningfilter116 may comprise any one or more elements to improve a profile ofbeam108 for treatment. In this regard, an intensity ofX-ray beam108 atbeam object30 may be highest at the center of the radiation field and may significantly decrease toward the edges of the field. Flatteningfilter116 may therefore be used to provide a more even intensity distribution.
• Control unit111 may be coupled to flatteningfilter116 so as to selectively place flattening filter in the path ofbeam108 for a treatment mode. Flatteningfilter116 may, however, increase an amount of radiation scattering, and therefore may not be suitable for an imaging mode of operation. Control unit111 may therefore also be coupled to flatteningfilter116 so as to selectively move flatteningfilter116 out of the path ofbeam108 for an imaging mode.
• Other elements117 may include shield blocks, dosimetry chambers, collimator plates, accessory trays and any other treatment, imaging, calibration, and verification devices as are known in the art. One or more ofother elements117 may be electrically and/or mechanically coupled to control unit111,operator console20, and/or to one or more other devices. For example, dosimetry chambers ofother elements117 may transmit dosimetric information directly tooperator console20. In another example, collimator plates ofelements117 may be driven to desired positions by a motor that is controlled byoperator console20.
• Operator console20 ofFIG. 2 may control an injector current produced byparticle source103, and/or an amount of power generated byRF power source107. Such control may include control oftrigger control106 to controlinjector105 orRF power source107, respectively.Operator console20 may also controlimaging device40 to acquire an image, and may control one or more elements oftreatment head101 via control unit111. Examples of the latter control according to some embodiments are provided below.
• FIG. 3 is a flow diagram of process steps60 according to some embodiments. Process steps60 may be executed by one or more elements oflinear accelerator10,operator console20,treatment head101, control unit111, and other devices. Accordingly, process steps60 may be embodied in hardware and/or software. Process steps60 will be described below with respect to the above-described elements, however it will be understood that process steps60 may be implemented and executed differently than as described below.
• Prior to step61, an operator may useinput device201 ofoperator console20 to initiate operation ofsystem1. In response,processor203 may execute program code of a system control application stored instorage204.FIG. 4 is an outward view of a user interface that is presented byoutput device202 in some embodiments due to execution of the program code.
• Interface80 may be used by an operator to input instructions tosystem1. Conversely,system1 may receive the instructions viainterface80. Embodiments may utilize one or more interfaces that share zero or more features withinterface80.
• In the illustrated embodiment,field81 indicates a status ofsystem1. As shown, the status indicates thatsystem1 is being programmed.Fields82 through86 indicate keys ofinput device201 that may be used to instructsystem1 to enter a selected operational mode. For example, function keys F1, F2, F3 and F4 (not shown) may be used to issue instructions to enter a low-energy photon radiation treatment mode, a high-energy photon radiation treatment mode, an electron radiation treatment mode, and an imaging mode, respectively.
• The selected mode is displayed infield87, with other details of the mode shown infields88 and89.Fields90 indicate a position ofgantry102 and a configuration of collimator plates ofelements117, whilefields91 through93 identify accessories mounted in each of three accessory trays ofelements117.Fields95 are reserved for presenting preset and actual values of dose (MON1 and MON2), beam on time (Time) and dose rate (MU/Min).
• Atstep61, the operator selects one of function keys F1 through F4 ofinput device201. It will initially be assumed that function key F4 is selected.FIG. 5 showsinterface80 after selection of function key F4 according to some embodiments.Fields87 and89 are automatically filled, while the operator may completefield88 and the top row offields95 directly or using sub-interfaces ofinterface80.
• Selection of function key F4 causes the labels offields82 through86 to change. According to the new labels, function keys F2, F3 and F4 may be used to control collimator plates ofelements117, and function key F1 may be used to access a sub-interface for specifying a desired dose.
• After completing all required fields ofinterface80 and of any sub-interfaces, an operator placessystem1 into a Ready mode by pressing an Accept key ofinput device201. According to the present example, detection of the pressing of the Accept key comprises receiving an instruction to enter a mode. Flow therefore proceeds to step62 after the Accept key is pressed.
• System1 determines whether an imaging mode or a treatment mode has been selected atstep62. Continuing with the present example, a focal spot size of a radiation beam is reduced at63 because an imaging mode has been selected. As described above, the focal spot size may be reduced by any suitable system to receivebeam108 and to change a focal spot size thereof. In some embodiments ofstep63, control unit111 energizes deflector plates ofbeam focuser112 such thatbeam108 will create a desired focal spot size on a target whenbeam108 is generated. In this regard, step63 may be performed prior to generation ofbeam108.
• A flattening filter is then moved out of a path of the radiation beam atstep64.FIG. 6 is a block diagram of system according to some embodiments. As shown, flatteningfilter116 has been moved from the position shown inFIG. 2 to a position out of the path ofbeam108. Any suitable mechanism may be employed to move flatteningfilter116 atstep64.
• Next, atstep65, a first target is replaced with a second target.FIG. 6 also showstarget115 occupying the position in the path ofbeam108 that was occupied bytarget114 inFIG. 2. In the illustrated embodiment,target114 may be replaced bytarget115 by movinghousing113 as shown. Any suitable systems for switchingtargets114 and115 may be employed.
• A scatter-reducing filter is moved into the path of the radiation beam at66.FIG. 6 shows scatter-reducingfilter118 in the path ofradiation beam108. Scatter radiation is believed to decrease image quality; therefore introduction of a scatter-reducing filter may increase image quality. The embodiment ofFIG. 2 does not include a scatter-reducing filter.
• An image is then acquired byimaging device40 atstep67. According to some embodiments ofstep67,linear accelerator10 is controlled to emitbeam108 towardtreatment head101 at a specified energy and dose rate.Beam108 is focused bybeam focuser112 to reduce a focal spot size thereof, and impacts target115 to generate a divergent photon beam having an energy spectrum suitable for imaging. The photon beam passes through scatter-reducingfilter118,other elements117, andbeam object30 before impactingimaging device40.Imaging device40 therefore acquires the image based on the photon beam as attenuated bybeam object30. In some embodiments,operator console20 updates the lower row offields95 ofinterface80 in real time during acquisition of the image.
• Steps63 through66 may be performed under the control of control unit111 in response to signals received fromoperator console20. For example,operator console20 may transmit a set of instructions and/or parameters associated with an imaging mode to control unit111 afterstep62. The set may be stored among one or more soft pots ofstorage204.
• In this regard, step61 may comprise reception of the set of instructions and/or parameters by control unit111 (or by another one or more elements for controlling elements of treatment head101). More generally, steps61 and62 may be performed by any element ofsystem1, may be performed at several times by different elements ofsystem1, and may be performed at any time prior to step67.Step63 through66 can also occur at any time beforestep67.
• Some embodiments include performance of only one, two, or three ofsteps63 through66. The steps of63 through66 that are performed may occur in any order relative to one another. Two or more ofsteps63 through66 may be performed simultaneously.
• FIG. 7 is a block diagram ofsystem1 prior to step67 according to some embodiments of process steps60.FIG. 7 is intended to illustrate some of the above-mentioned possible variations of process steps60. As shown,beam focuser112 is positioned outside of the path ofradiation beam108.Beam focuser112 according to the illustrated embodiment comprises a device that increases a focal spot size ofbeam108, thereforebeam focuser112 is moved out of the path in order to reduce the focal spot size atstep63.
• TheFIG. 7 embodiment reflects the completion ofsteps64 and65 as described below. However,step66 is not performed with respect to theFIG. 7 embodiment becausesystem1 ofFIG. 7 does not include a scatter-reducing filter.
• FIG. 8 is a block diagram ofsystem1 prior to step67 according to still other embodiments of process steps60. As shown,beam focuser112 is positioned in and flatteningfilter116 is moved out of the path ofradiation beam108 to operate as described with respect to step63,step64, andFIG. 6. TheFIG. 8 embodiment includes only a single hi-Z target114 and therefore does not performstep65 of process steps60. Moreover,system1 ofFIG. 8 does not include a scatter-reducing filter, and therefore step66 is not performed with respect to theFIG. 8 embodiment.
• Flow returns to step61 afterstep67. It will now be assumed that an instruction to enter a treatment mode is received atstep61. The instruction may be received in response to operator selection of function keys F1 through F3 during presentation ofinterface80 ofFIG. 4.
• FIG. 9 illustratesinterface80 after selection of function key F2 (X-FIX-L) according to some embodiments. Function key F2 is associated with low-energy X-ray treatment, therefore fields87 and89 are automatically filled to indicate such treatment. The operator may completefield88 and the top row offields95 using sub-interfaces associated with the new labels offields82 through86.
• As described above, an operator may placesystem1 into a Ready mode by pressing an Accept key ofinput device201 after completing all required fields ofinterface80 and of any sub-interfaces. Detection of the depressed Accept key may also comprise receiving an instruction to enter a mode atstep61.
• Next, atstep62, it is determined thatsystem1 has been instructed to enter a treatment mode. Accordingly, flow continues to step68 to increase a focal spot size of a radiation beam. The focal spot size may be increased by deactivating or removing a beam focuser otherwise operable to reduce the focal spot size, or by placing a beam focuser for increasing the focal spot size in the path of the beam.FIG. 2 illustrates the former scenario, withbeam focuser112 being deactivated atstep68.
• FIG. 2 also illustrates flatteningfilter116 having been moved into the path ofbeam108 atstep69, and replacement oftarget115 withtarget114 atstep70. Some embodiments of process steps60 further include movement of a scatter-reducing filter out of the path of the radiation beam atstep71. The embodiment ofFIG. 2 does not include a scatter-reducing filter.
• System1 executes radiation treatment atstep72. According to some embodiments ofstep72,linear accelerator10 is controlled to emitbeam108 towardtreatment head101 at a specified energy and dose rate suitable for radiation treatment. The specified energy may be substantially identical to the energy used to acquire the image atstep67, and the dose rate may be significantly larger.Beam108 then impactstarget114 to generate a divergent photon beam having an energy spectrum suitable for treatment. The photon beam passesother elements117 andbeam object30 to deliver a radiation dose to a target volume ofbeam object30. In some embodiments,operator console20 updates the lower row offields95 ofinterface80 as shown inFIG. 9 during treatment.
• As described with respect tosteps63 through66, steps68 through71 may be performed under the control of control unit111 in response to signals received fromoperator console20. Such control may include transmission of a set of instructions and/or parameters associated with radiation treatment to control unit111 afterstep62. The set may be stored among one or more soft pots ofstorage204.
• Some embodiments such as that shown inFIG. 2 include performance of only one, two, or three ofsteps68 through71. The steps of68 through71 that are performed may occur in any order relative to one another. Two or more ofsteps68 through71 may be performed simultaneously.
• According to some embodiments, dosimetric characteristics ofbeam108 may be changed in response to an instruction to enter an imaging mode and/or in response to an instruction to enter a treatment mode. For example, in response to an instruction to enter an imaging mode,RF power source107 and/or bendingenvelope109 may be controlled as described in commonly-assigned, co-pending Application Serial No. (Attorney Docket No. 2005P00148US), entitled Megavoltage Imaging System, such thatbeam108 possesses characteristics suitable for imaging.
• The several embodiments described herein are solely for the purpose of illustration. Therefore, persons in the art will recognize from this description that other embodiments may be practiced with various modifications and alterations.

Claims (19)

1. A method comprising:

receiving a first instruction to enter an imaging mode;

in response to the first instruction, automatically performing at least one of: reducing a focal spot size of a radiation beam, moving a flattening filter out of a path of the radiation beam, replacing a first target for photon emission with a second target for photon emission, or moving a scatter-reducing filter into the path of the radiation beam;

receiving a second instruction to enter a first radiation treatment mode; and

in response to the second instruction, automatically performing at least one of: increasing a focal spot size of the radiation beam, moving the flattening filter into the path of the radiation beam, replacing the second target with the first target, or moving the scatter-reducing filter out of the path of the radiation beam.

2. A method according toclaim 1, wherein the second instruction comprises an instruction to enter a photon radiation treatment mode, and further comprising:

receiving a third instruction to enter an electron radiation treatment mode; and

in response to the third instruction, automatically moving the first target or the second target out of the path of the radiation beam so that neither the first target or the second target is in the path of the radiation beam.

3. A method according toclaim 1, wherein reducing the focal spot size of the radiation beam comprises energizing deflector plates disposed adjacent to the path of the radiation beam to focus the radiation beam.

4. A method according toclaim 1, wherein an atomic weight of the second target is less than an atomic weight of the first target.

5. A method according toclaim 1, wherein, for a given incident electron beam, photons emitted by the second target exhibit a lower average energy than photons emitted by the first target.

6. A method according toclaim 1, further comprising:

presenting an interface to receive the first instruction and the second instruction.

7. A method according toclaim 1, further comprising:

in response to the first instruction, automatically changing dosimetric characteristics of the radiation beam.

8. An apparatus comprising:

an input device to receive a first instruction to enter an imaging mode, and a second instruction to enter a first radiation treatment mode;

an accelerator waveguide to emit a radiation beam; and

at least one of:

a first device to reduce a focal spot size of a radiation beam in response to the first instruction, and to increase a focal spot size of the radiation beam in response to the second instruction;

a second device to move a flattening filter out of a path of the radiation beam in response to the first instruction, and to move the flattening filter into the path of the radiation beam in response to the second instruction;

a third device to replace a first target for photon emission with a second target for photon emission in response to the first instruction, and to replace the second target with the first target in response to the second instruction; or

a fourth device to move a scatter-reducing filter into the path of the radiation beam in response to the first instruction, and to move the scatter-reducing filter out of the path of the radiation beam in response to the second instruction.

9. An apparatus according toclaim 8, the first device comprising:

deflector plates disposed adjacent to the path of the radiation beam.

10. An apparatus according toclaim 8, wherein an atomic weight of the second target is less than an atomic weight of the first target.

11. An apparatus according toclaim 8, wherein, for a given incident electron beam, photons emitted by the second target exhibit a lower average energy than photons emitted by the first target.

12. An apparatus according toclaim 8, further comprising:

a fifth device to change dosimetric characteristics of the radiation beam in response to the first instruction.

13. A medium storing program code, the program code comprising:

code to receive a first instruction to enter an imaging mode;

code to, in response to the first instruction, automatically perform at least one of: reduce a focal spot size of a radiation beam, move a flattening filter out of a path of the radiation beam, replace a first target for photon emission with a second target for photon emission, or move a scatter-reducing filter into the path of the radiation beam;

code to receive a second instruction to enter a first radiation treatment mode; and

code to, in response to the second instruction, automatically perform at least one of: increase a focal spot size of the radiation beam, move the flattening filter into the path of the radiation beam, replace the second target with the first target, or move the scatter-reducing filter out of the path of the radiation beam.

14. A medium according toclaim 13, wherein the second instruction comprises an instruction to enter a photon radiation treatment mode, and the program code further comprising:

code to receive a third instruction to enter an electron radiation treatment mode; and

code to, in response to the third instruction, automatically move the first target or the second target out of the path of the radiation beam so that neither the first target or the second target is in the path of the radiation beam.

15. A medium according toclaim 13, wherein the code to reduce the focal spot size of the radiation beam comprises code to energize deflector plates disposed adjacent to the path of the radiation beam to focus the radiation beam.

16. A medium according toclaim 13, wherein an atomic weight of the second target is less than an atomic weight of the first target.

17. A medium according toclaim 13, wherein, for a given incident electron beam, photons emitted by the second target exhibit a lower average energy than photons emitted by the first target.

18. A medium according toclaim 13, the program code further comprising:

code to present an interface to receive the first instruction and the second instruction.

19. A medium according toclaim 13, the program code further comprising:

code to, in response to the first instruction, automatically change dosimetric characteristics of the radiation beam.

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